A seat slide device has lower rails attached to a floor of a vehicle, and upper rails provided slidably on the lower rails and coupled to the seat frames (see Patent Documents 1 to 5). A lock mechanism is provided on the seat slide device, which is used by releasing locking and slide-adjusting a relative position of the upper rails with respect to a longitudinal direction of the lower rails, and locking at a desired position.
On the other hand, for vehicle seats, weight reduction is constantly demanded for fuel consumption improvement in view of energy conservation. Regarding seat main bodies, the present applicant has hitherto made various proposals on technology related to weight reduction. For example, the applicant proposed one having a structure in which a three-dimensional knitted fabric is strained as respective cushion members of a seat back part and a seat cushion part (see Patent Document 6), instead of urethane materials which are generally used widely.